Synthetic resins, including polyesters and aliphatic and aromatic polyamides, such as nylon-6,6 and nylon-6, and copolymers thereof, are often used for molded articles and fibers. In many uses, particularly for molded articles, it is preferred if the resin has improved resistance to fire, compared to the resin alone. This is often attained by the addition of various agents which improve the basic fire resistance (i.e., flame retardance) of the resin, but sometimes these agents degrade or diminish other physical properties of the resin. Since resins are widely used, compositions which have improved fire resistance but yet retain the desirable physical properties of the resin are constantly being sought.
German Patents 2,150,484 and 2,130,793, and A. E. Lipska, Comb. Inst. Arizona State Univ., West. State Sect. Combust, Inst. WSCI, 1973, report that certain tungsten compounds can be used in various ways to improve the fire resistance of polyamides. The combinations of agents described hereinafter are not disclosed in these references.
U.S. Pat. No. 4,298,518 discloses compositions containing polyamides and melamine cyanurate, which are said to have good fire resistance.
U.S. Pat. No. 3,458,470 discloses compositions containing polyamides and a variety of tungsten or molybdenum compounds, including silico- and phospho-tungstic acids. These compositions are said to have good resistance to discoloration and be stable to light.
Melamine phosphate may be added to synthetic resins to improve the flame retardancy of the resins, but when heated to normal engineering polymer processing temperatures the melamine phosphate gives off so much water that the resultant mixture of the resin and the melamine phosphate has very poor physical properties.
What are needed. therefore, are flame retardant resin compositions which do not have the problems and deficiencies of the prior art.